/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/Selection/GeometrySelector.h
Compute a 3D frame for the provided Selection. For example this could simply be a frame aligned to the XYZ axes at the center of the selection bounding-box, or something more sophisticated, like aligned to the tangent-space of the selected element(s), etc.
void GetSelectionFrame ( const [FGeometrySelection](API\Plugins\ModelingComponents\Selection\IGeometrySelector\FGeometrySelection) & Selection, [UE::Geometry::FFrame3d](API\Runtime\GeometryCore\FFrame3d_1) & SelectionFrameOut, bool bTransformToWorld )